1. Field of the Invention
The present invention relates to an image forming apparatus, such as a copying machine or a printer, having a plurality of feed openings, and particularly to an image forming apparatus which uses any of the feed openings as a preferential feed opening, assigned priority in selection among them.
2. Description of the Prior Art
An image forming apparatus such as a copying machine, having a plurality of feed openings is generally designed such that a specified feed opening is always set first at the time of turn-on of a main switch or automatic resetting.
A cassette containing sheets of paper of the most frequently used size is usually attached to such specified feed opening, i.e., the preferential feed opening. Accordingly, such design is convenient for use since paper sheets of a frequently used size (for example, the A4 size or the B4 size) are enabled to be automatically fed.
However, the preferential feed opening in a conventional image forming apparatus such as a copying machine is fixedly set and accordingly a transport system for transporting paper from the preferential feed opening to an image forming portion tends to be excessively used. As a result, feed rollers or the like for the preferential feed opening would be worn out quickly and paper jam in that transport system would occur frequently. Thus, convenience provided by setting of the preferential feed opening causes rather adverse influence and the preferential feed opening becomes inconvenient to the user on the contrary.
In addition, it happens that paper jam also occurs frequently in other feed openings than the preferential feed opening due to any trouble in the transport system concerned or the like. In such feed opening liable to cause paper jam is continuously used, paper jam occurs frequently, which causes great inconvenience.
In order to avoid jam of paper of a frequently used size, a cassette containing paper sheets of the frequently used size may be attached to a feed opening other than a preferential feed opening. However, such a method increases the number of operations required for changing feed openings, for example, pressing of a paper size selection button or the like each time in the initial mode, which causes inconvenience to the user and also causes erroneous operation of a print switch as a result of erroneous designation of a paper size.
On the other hand, an image forming apparatus such as a copying machine, provided with a plurality of feed openings and a feed opening selection switch of a rotation system for successively selecting the feed openings in the order of priority, is generally adapted to have the above stated order of priority fixedly determined. Such an apparatus is designed so that a feed opening assigned a first priority is automatically set at first when a main switch is turned on or automatic resetting is effected. In this case, the same disadvantages as in the preferential feed opening in the above described image forming apparatus are involved in the feed opening assigned the first priority.